The Future (53 page)

The growing absorption of CO
₂
in the oceans also interferes with the reproduction of some species. And among the shell-making creatures at risk are tiny zooplankton with
very thin shells that play an important role at the bottom of the ocean food chain. Although much research remains to be done, many scientists are concerned about what has been happening to this crucial link that lies at the base of the ocean food chain.

Some areas of the ocean, including some off the coast of
Southern California that have been sampled, are actually
corrosive
. In coastal areas of Oregon, newly corrosive seawater is
killing commercially valuable shellfish. Experts have noted that even if human-caused CO
₂
emissions were somehow ended in the near term, it would take tens of thousands of years before the chemistry of the
oceans returned to a state comparable to that which existed prior to the last century.

Global warming and CO
₂
-caused acidification are exacerbating declines
in fisheries and marine biodiversity that have already been caused by other human activities, such as overfishing. According to the United Nations,
almost a third of all fish species are presently overexploited. Overfishing, described in
Chapter 4
, has already led to the dangerous
depletion of up to 90 percent of large fish like tuna, marlin, and cod.

Some fishing techniques such as dynamite fishing (which still takes place in some developing countries with coral reefs) and bottom trawling (the northeast Atlantic has been particularly damaged by this practice) do extra damage to the ocean ecosystems important to the survival of sea life. Although there have been some notable success stories in some ocean fisheries, the overall picture is still extremely troubling. The combination of many factors poses a synergistic threat to the continued health of the oceans.

Along with coral reefs,
critical ocean habitats like mangrove forests in many coastal areas and so-called
sea grass meadows are also at risk. In addition, the number of dead zones growing in the oceans
near the mouths of major river systems is doubling every decade. The heavy concentrations of nitrogen and phosphorus contained in agricultural runoff water and wastewater feed algae growth and when the algae are consumed by bacteria, the large areas of the ocean are completely depleted of oxygen, leading to the dead zones.

Ironically, the historic North American drought of 2012 reduced the flow of water from the Mississippi into the Gulf of Mexico so much—and the nitrogen, phosphorus, and other chemicals normally carried with the water—that the
large dead zone spreading from the mouth of the Mississippi began to temporarily clear up.

A conference of ocean experts meeting at Oxford University in the summer of 2011 reported their conclusions as a group: “This examination of synergistic threats leads to the conclusion that we have underestimated the overall risks and that the whole of marine degradation is greater than the sum of its parts, and that degradation is now happening at a faster rate than predicted.… When we added it all up, it was clear that we are in a situation that could lead to major extinctions of organisms in the oceans.… It is clear that the traditional economic and consumer values that formerly served society well,
when coupled with current rates of population increase, are not sustainable.”

For at least three decades, there has been a debate in the international community about the relative importance of reducing greenhouse gas emissions to
mitigate
the climate crisis compared to strategies for
adapting
to the climate crisis. Some of those who try to minimize the significance of global warming and oppose most of the policies that would mitigate it often speak of adaptation as a substitute for mitigation.

They promote the idea that since humankind has adapted to every environmental niche on the planet, there is no reason to believe that we shouldn’t merely accept the consequences of global warming and get busy adapting to them. For example, the CEO of ExxonMobil, Rex Tillerson, recently said in an exchange provoked by longtime activist David Fenton, “
We have spent our entire existence adapting, OK? So we will adapt to this.”

F
OR MY OWN
part, I used to argue many years ago that resources and effort put into adaptation would divert attention from the all-out push that is necessary to mitigate global warming and quickly build the political will to sharply reduce emissions of global warming pollution. I was wrong—not wrong that deniers would propose adaptation as an alternative to mitigation, but wrong in not immediately grasping the moral imperative of pursuing both policies simultaneously, in spite of the difficulty that poses.

There are two powerful truths that must inform this global discussion about adaptation and mitigation: first, the consequences that are already occurring, let alone those that are already built into the climate system, are particularly devastating to low-income developing countries. Infrastructure repair budgets have already skyrocketed in countries where roads, bridges, and utility systems have been severely
damaged by extreme downpours and resulting floods and mud slides. Others have been devastated by the climate-related droughts.

And the disruptions of subsistence agriculture by both the floods and the droughts have led to
skyrocketing expenditures for food imports in many developing countries. Also, as noted earlier, some low-lying nations are also already struggling to relocate refugees from coastal areas affected
by the early stages of sea level rise, while other
nations are struggling to integrate arriving refugee groups into already fast-growing populations.

Since these and other developments will not only continue but worsen, the world does indeed have a moral duty and practical economic necessity to assist these nations with adaptation. Disturbingly, the world has yet to fully realize the effects of the global warming pollution already in the atmosphere. Even if we drastically reduce our emissions today,
another degree Fahrenheit of warming is already “in the pipeline” and will manifest itself in the coming years. In other words, so many harmful changes are already built into the climate system by the enormous increase in the emissions, and particularly the increased
concentration
, of greenhouse gases in the atmosphere that adaptation is absolutely essential—even as we continue building the global political consensus needed to prevent the worst consequences from occurring. We have no choice but to pursue both sets of policies simultaneously.

But the second truth that must inform this debate is still by all odds the most powerful imperative: unless we quickly start reducing global warming pollution, the consequences will be so devastating that adaptation will ultimately prove to be impossible in most regions of the world. For example, higher greenhouse gas emissions are already beginning to cause
large-scale changes in atmospheric circulation patterns and are predicted to bring almost unimaginably deep and prolonged drought conditions to a wide swath of highly populated and agriculturally productive regions, including all of Southern and south-central Europe, the Balkans, Turkey, the southern cone of Africa, much of Patagonia, the populated southeastern portion of Australia, the American Southwest and a large portion of the upper Midwest, most of Mexico and Central America, Venezuela and much of the northern Amazon Basin, and significant portions of Central Asia and China.

The scientific reasoning behind this devastating scenario requires some explanation. The basic nature of the global climate system, when viewed holistically, is that it serves as an engine for redistributing heat energy: from the equator toward the poles, between the oceans and the land, and from the lower atmosphere to the upper atmosphere and back again. The large increase in heat energy trapped in the lower atmosphere means—to state the obvious—that the atmospheric system is becoming more energetic.

In the northern hemisphere, this climate engine transfers heat energy from south to north in the Gulf Stream—which is the best known component of the so-called ocean conveyor belt, a Möbius Strip–like loop that connects all of the world’s oceans. Other components include deep currents that travel along the bottom of the ocean, redistributing cold water from the poles back to the equator, where they return to the ocean surface. The largest of these are the Antarctic circumpolar current, which travels around the Antarctic continent and
feeds the shallower Humboldt current, which flows from the Southern Ocean northward along the west coast of South America and upwells—laden with nutrients—to nourish the rich concentration of sea life off the coast of Peru; and, less well known, the deep cold current that travels north to south from an area of the North Atlantic in the vicinity of southern Greenland,
underneath
the Gulf Stream, back to the tropical Atlantic waters.

Energy is also redistributed by cyclones, by thunderstorms, and by multiyear patterns such as the alternating El Niño/La Niña phenomenon (known to scientists as the ENSO, or El Niño/Southern Oscillation). Moreover, all of these energy transfers are affected by the Coriolis effect, which is driven by the spinning of the Earth on its axis, from west to east.

Until recently, relatively less attention has been paid to the relationship between global warming and the atmospheric patterns that move energy vertically up and down in the atmosphere. The so-called Hadley cells spanning the tropics and subtropics are enormous barrel-shaped loops of wind currents that circle the planet on both sides of the equator, like
giant pipelines through which the trade winds flow from east to west.

Warm and moist wind currents rise from the ground vertically into the sky in both of these cells at the edge of each respective loop that is adjacent to the equator. When their ascent reaches the top of the troposphere (the top of the lower atmosphere, approximately ten miles high in the tropics), each loop turns poleward—which means northward in the northern hemisphere cell and southward in the other. By the time these currents reach the top of the sky, much of the
moisture they carried upward has fallen back to the ground as rain in the tropics.

At the apex of its ascent, each of these air currents starts flowing
poleward along the top of the troposphere and travels about 2,000 miles (approximately 30 degrees of latitude), until it has discharged most of its heat. Then it descends vertically as a cooler and much drier downdraft. When each loop reaches the surface again, it turns back toward the equator, recharging itself with heat and moisture as it travels across the surface of the Earth. As it returns to the equator, it completes its loop and repeats the cycle by rising vertically once again,
laden once more with heat and water vapor.

As a result of the dry downdrafts of the Hadley cells, the areas of the Earth 30 degrees north and 30 degrees south of the equator are highly vulnerable to desertification. Most of the driest regions of the Earth, including the largest of the planet’s deserts, the Sahara,
are located under these dry downdrafts. (Other factors contributing to the location of deserts include
the “rain shadows” of mountain ranges—the areas downwind from mountain peaks—because the prevailing winds rise when they hit the windward side of the mountains and lose their moisture before descending as dry downdrafts on the leeward side. In addition, the location of deserts is influenced by
what geographers call continentality—which means that the areas in the middle of large continents typically get much less moisture because they are farther away from the oceans.) But on a global basis, the most powerful desertifying factor is the
downdraft of the Hadley cells.

The problem—which climate scientists have long predicted with computer models and are now observing in the real world—is that the massive warming of the atmosphere is changing the locations of these great global downdrafts, moving them farther away from the equator and toward the poles, thus widening the subtropics and intensifying their aridity. Indeed, in the northern hemisphere, the downdraft has already moved northward by as much as 3 degrees latitude—approximately 210 miles—although measurements are still imprecise. The downdraft of the Hadley cell
south of the equator has also moved poleward.

There are several
theories for why global warming is causing a shift in the Hadley cells, none of which are as yet confirmed. The solar heating of the lower atmosphere in the tropics and subtropics is much greater than anywhere else on the planet for obvious reasons: the sunlight strikes the Earth at a more direct angle all year round. On a percentage basis, surface temperatures are rising faster in the higher latitudes because the
melting of ice and snow is dramatically changing the reflectivity of the surface,
^‡
thereby increasing the absorption of heat energy. This means, among other things, that
the difference in average temperatures between the tropics and the polar regions is diminishing over time—which also has consequences for the climate balance.

However, the much larger amounts of overall heat energy absorbed in the mid-latitudes is still much greater, and causes the warmer (and thus less dense) air in the tropics to rise higher. As a result, the extra heat raises the top of the troposphere, where the wind currents deflect at a right angle from their vertical trajectory and begin traveling poleward.

The widening of the Hadley cells moves the downstroke of its circular path farther north in the northern hemisphere and farther south in the southern hemisphere. As with many of the realities connected to global warming, while this one sounds technical and can seem abstract, the real consequences for real people, animals, and plants are extremely severe.

For the areas now subjected to this downdraft, it’s a bit like being under a giant hairdryer in the sky. The results include not just more frequent and more severe droughts, but
consistent
drought patterns likely leading to desertification in many of the countries in the line of fire. Moreover, most of the areas affected, like Southern Europe, Australia, Southern Africa, the American Southwest, and Mexico—are already
on the edge of persistent water shortages anyway.